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Re: Tertiary mammals in the Cretaceaous



On  Sat, 22 Feb 1997 John Bois wrote:

> Do you think we will find any other modern-aspect mammals in existence
> befor the K/T?
> Do you think the ones we know about were strictly micro niche animals?
> Do we find burrows anywhere?

As fas as I know, very few mammals which belong to modern orders have 
been found in the Cretacous. A primitive primate (?) (Purgatorius) 
has been found in North American Latest Cretaceous strata, but it has 
been suggested that the few specimens are Paleocene in age 
and have been mixed up with Cretaceous material. In addition, it is 
not at all sure that the group Plesiadapoidea to which Purgatorius 
belongs are indeed primitive primates.

In Australia, two Cretaceous monotremes (which were obviously more 
diverse in the Late Cretaceous and Early Tertiary than they are 
today) have been found. One of them (Steropodon) is a relative of the 
modern platypus, the other one was recently described in Nature and belongs to 
an 
extinct group (I can't recall its name).

In South America another primitive ungulate, Perutherium,  has been found in a
probably Cretaceous locality (Laguna Umayo). It belongs to a group 
(Notoungulata) which flourished in South America during much of the 
Tertiary but is extinct today, however it is still a 'modern-aspect' 
mammal for the Cretaceous.

In the Cretaceous of Asia primitive placental mammals have been found which are 
possibly related to rodents and lagomorphs (rabbits etc.), but I am 
not well informed about them. Perhaps someone else knows better 
whether they are really their relatives.

As far as I know, the only place on earth where Latest Cretaceous 
mammals are well documented is North America (with the Bug Creek 
and Harbicht Hill faunas), so it is not at all astonishing that we 
know only a handful of mammals of modern aspect. However, I am sure 
that more of them were existing and will, as I hope, eventually be 
found. The origin of many groups of modern  mammals is still unknown or 
questionable, but it has been speculated that many of them already 
developed in the Cretaceous.

Most of the known animals were small. (The exception are the 
Australian monotremes, which were already  medium-sized.) 
Usually, only their teeth have been found, so we know very little 
about what they looked like or how they lived, but I can't imagine 
that all of them were nocturnal. I do not know of 
any burrows that have been found, but this is not surprising as most 
fossils have been found in sediments formed by river channels.

Martin Jehle